The present invention relates generally to the protection of metallic surfaces from scaling and the accumulation of other deposits. More specifically, the present invention relates to scale inhibiting compositions, dispersants and methods of using the same.
To efficiently transfer heat from a metal surface, such as the inside surface of a boiler or heat exchanger tube, to any liquid medium such as water, or vice versa, the surface of the metal should be as clean and as free of scales and deposits as possible. Simply put, scaling and other deposits on the metal surface will reduce the rate of heat transfer between the metal surface and the water or other fluid medium and therefore scaling and deposits will reduce the efficiency of the system. Further, scaling and deposits can lead to premature corrosion of metallic surfaces.
The most common way to combat scaling and deposit accumulation in aqueous systems is to add scale-inhibiting additives and dispersants to the feedwater or solution. However, currently available scale-inhibiting additives and dispersants are non-biodegradable, which limits the applicability of such additives.
Scaling and deposits in industrial heat exchange systems may come in a variety of forms and originate from a variety of sources. Typically, scales and deposits are caused by calcium ions, magnesium ions, iron ions, zinc ions and clay particulates.
More specifically, said scales and deposits include but are not limited to alkaline earth metal phosphates, alkaline earth metal carbonates, alkaline earth metal sulfates, iron (hydro)oxides, zinc hydroxides, manganese oxides, aluminum (hydro)oxides, clays and silicates.
For example, industrial water, such as the water used in cooling towers, heat exchangers and boilers, is often treated with a variety of inorganic and organic phosphorus-containing compounds. These compounds tend to produce calcium phosphate and magnesium phosphate scales which adhere to cooling tower surfaces, heat exchanger tubes, and boiler surfaces.
Further, soluble iron may be introduced into an aqueous system by its presence in the feedwater or in other ways. Soluble iron is generally believed to be iron in the form of Fe.sup.++. Soluble iron, as this term is used herein, does not exclude, however, other forms of iron that are soluble in a given water system. In aqueous systems, and particularly industrial aqueous water systems, the presence of soluble iron in the feedwater, or the introduction of a soluble iron species into the system by other means such as corrosion, can lead to the undesirable precipitation of iron oxides and iron hydroxides which may settle and accumulate as deposits on surfaces that come in contact with the water. Such precipitates commonly occur where water containing soluble iron ions is changed to a more oxidation-prone environment. Also, precipitation will occur where an oxidizing agent such as oxygen, chlorine and the like is introduced or increased.
Further, many industrial water systems such as those used in the operation of cooling towers are treated with soluble zinc salts. Such soluble zinc salts tend to form undesired scales in alkaline solutions or in the presence of other precipitating anions such as phosphate.
Finally, clay particulates may be introduced into an aqueous system by the presence of clay in the feedwater. Accumulation of clay particulates tends to form deposits on metallic heat exchangers or metal surfaces of boilers.
The aforementioned scales and deposits reduce heat transfer, accelerate corrosion or cause other problems resulting in reduced system efficiencies.
Currently, certain polyacrylates and polyacrylamides are used to inhibit the build-up of scales in aqueous systems. However, polyacrylates and polyacrylamides are not biodegradable and thus accumulate in the environment upon release from the water treatment systems. Thus, there is need for biodegradable compositions that are capable of inhibiting the build-up of scales and deposits on metallic surfaces. Although polyaspartic acid is biodegradable, it does not effectively inhibit the build-up or scales and deposits on metallic surfaces.